/Engine/Source/Runtime/Engine/Classes/Engine/RuntimeOptionsBase.h
You can also change the name of the ini file that settings are gathered from in your derived UCLASS() declaration
class URuntimeOptionsBase : public [UObject](API\Runtime\CoreUObject\UObject\UObject)
FString
OptionCommandPrefix
The command prefix for all options declared in a subclass (defaults to "ro", so a property named TestProp would be exposed as ro.TestProp)